Display optimization techniques for micro-led devices and arrays

ABSTRACT

Systems and methods to achieve desired color accuracy, power consumption, and gamma correction in an array of pixels of a micro-LED display. The method and system provides an array of pixels, wherein each pixel comprising a plurality of sub-pixels arranged in a matrix and a driving circuitry configured to provide an individual emission control signal to each sub-pixel of each pixel in the array of pixels to independently control an emission time and a duty cycle of each sub-pixel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 17/015,024, filed Sep. 8, 2020, now allowed, which is acontinuation of U.S. Nonprovisional application Ser. No. 16/126,444,filed Sep. 10, 2018, abandoned, which claims the benefit of U.S.Provisional application Ser. No. 62/556,608, filed Sep. 11, 2017, eachof which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present disclosure relates generally to micro LED displays and, moreparticularly, to a micro LED display system and method for improvingdynamic range, power consumption and color and gamma correction of themicro LED display.

SUMMARY

Briefly stated, technologies are generally described herein to achievedesired color accuracy, power consumption, and gamma correction in anarray of pixels of a micro-LED display. Using the technologies describedherein, either the duty cycles or the emission times of sub-pixelsarranged in a matrix for each pixel of the micro-LED display may beadjusted to tune the display color without affecting the gamma.

According to one embodiment, a display device may be provided. Thedisplay device may include an array of pixels, wherein each pixel maycomprising a plurality of subpixels arranged in a matrix. The displaydevice may also include a driving circuitry configured to provide anindividual emission control signal to each sub-pixel of each pixel inthe array of pixels to independently control an emission time and a dutycycle of each sub-pixel.

According to other embodiment, a method for controlling a pixel circuitof an array of pixel circuits of a display device comprising a pluralityof subpixels may include providing an individual emission control signalto each sub-pixel of each pixel in the array of pixel circuitsindependently to control an emission time and a duty cycle of thesub-pixels.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional aspects and embodiments of the presentdisclosure will be apparent to those of ordinary skill in the art inview of the detailed description of various embodiments and/or aspects,which is made with reference to the drawings, a brief description ofwhich is provided next.

FIG. 1a is a circuit diagram showing individual emission (EM) controlsignal for sub-pixel elements.

FIG. 1b is a timing diagram illustrating an example of three differentemission time created by three individual EM signal.

FIG. 1c is a timing diagram illustrating an example of controlling theemission time of each sub-pixel.

FIG. 2a-2b diagrammatic illustrations of a power optimized displaydriving scheme.

While the present disclosure is susceptible to various modifications andalternative forms, specific embodiments or implementations have beenshown by way of example in the drawings and will be described in detailherein. It should be understood, however, that the disclosure is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of an invention as defined by theappended claims.

DETAILED DESCRIPTION Color Share and Gamma Adjustment

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

As used in the specification and claims, the singular forms “a”, “an”and “the” include plural references unless the context clearly dictatesotherwise.

The term “comprising” as used herein will be understood to mean that thelist following is non-exhaustive and may or may not include any otheradditional suitable items, for example one or more further feature(s),component(s) and/or element(s) as appropriate.

In this description, the term “sub-pixel” and “micro device” are usedinterchangeably. However, it is clear to one skill in the art that theembodiments described here are independent of the device size. Eachpixel and sub-pixel used in the description is a light emittingmicro-device (Micro-LED).

Micro-LEDs, in general, tend to have a nonlinear current-luminanceefficiency (Cd/A) as a function of the drive current. Thischaracteristic may often include a peak of efficiency at a certaincurrent level. A display module may consists an array (active orpassive) of pixels. Each pixel itself may comprised of multiplesub-pixels (RGB, RGBW, RGBY, or other combination of color elements,e.g. blue with light conversion). In order to get a target “white-point”(W_(x,y)), it may be required to mix certain ratios of the colorelements. For instance, for given Red (R_(x,y)), Green (G_(x,y)), andBlue (B_(x,y)) elements, one can use share factors to create the wantedcolor based on the sum of all the sets, such as

K_(R).R_(x,y)+K_(G).G_(x,y)+K_(B).B_(x,y)=W_(x,y)   (1)

where Ki's are the share factors for the tri-color set and x,y are twocolor coordinates that specify a point on a CIE chromaticity diagram,which represents the mapping of human color perception in terms of thetwo CIE parameters x and y.

In some applications, it may be required to drive the micro-LEDs at thecurrent level corresponding to the peak efficiency. In this scenario,the desired output luminance level may be achieved using modulationtechniques, e.g. Pulse Width Modulation (PWM). Accordingly, a duty-cycleof the emission (EM) control signal will determine the luminance level.However, in order to achieve the desired white-point, one cannot applythe same duty cycle to each of the color elements. The duty-cycle refersto the total amount of time a pulse is ‘on’ over the duration of thecycle/frame.

FIG. 1a is a circuit diagram showing individual EM signals for sub-pixelelements. The driving circuitry 100 includes a plurality of emissioncontrol signals (102, 104, 106) and a plurality of data lines (108, 110,112) extending to a pixel 120 having a plurality of sub-pixels elements(114, 116 and 118).

As shown in FIG. 1 a, instead of providing combined emission control foreach pixel 120, a driving circuitry 100 consisting of three individualEM control signals EM_(R) 102, EM_(G) 104, and EM_(B) 106 for eachsubpixel (R 114, G 116, B 118) may be provided to facilitateproportional contribution of color elements. The driving circuitry 100may be configured to provide an individual emission control signal toeach sub-pixel of each pixel in the array of pixels to independentlycontrol an emission time and a duty cycle of the sub-pixels.

By controlling emission control signals EM_(R) 102, EM_(G) 104 andEM_(B) 106 of sub-pixels rather than pixels, a desired luminance may beachieved. Thus, a first emission control signal e.g. EM_(R) 102 isprovided concurrently to each sub-pixel of a first color in at least onerow of pixels, a second emission control signal e.g. EM_(G) 104 isprovided concurrently to each sub-pixel of a second color in at leastthe one row of pixels, and a third emission control signal e.g. EM_(B)106 is provided concurrently to each sub-pixel of a third color in atleast the row of pixels. The first color may be provided as red, thesecond color may be provided as green, and the third color may beprovided as blue.

In one embodiment, a fourth emission control signal may be provided toeach sub-pixel of a fourth color in at least one row of pixels in thearray of pixels, wherein the fourth color is one of cyan, white, andyellow. The emission control signal may be a pulse-width-modulation(PWM) signal.

FIG. 1b is a timing diagram illustrating an example of three differentemission time created by three individual EM signals EM_(R) 102, EM_(G)104 and EM_(B) 106. Here, a frame may start with a off time due toprogramming or another requirement. Then, the three EM control signals102, 104, 106 of subpixels are enabled. In one case, all three emissionsignals may be enabled at the same time, or they may be enabled atdifferent time during a frame time 120. In an example as demonstrated inFIG. 1b , the first color (e.g. red) has longer emission time 126 tooperate at its peak efficiency and meeting display requirements. Thesecond color (e.g. green) has a shorter emission time 124 and the thirdcolor (e.g. blue) can have a different emission time 122 as well.Despite simplicity, the main challenge with this approach can be thecolor mixing.

To address this challenge, each emission is turned on and off multipletimes at different duty cycle during the frame time 120 as demonstratedin FIG. 1c . FIG. 1c is a timing diagram illustrating an example ofcontrolling the emission time of each sub-pixel. As shown in FIG. 1c ,different duty cycles 132, 134, and 136 are used for controlling theemission time of each subpixels. Moreover, there can be black framebefore or after a combination of few toggles.

Either the duty cycles 132, 134, 136 or the emission times 122, 124, 126as demonstrated in FIG. 1b and FIG. 1c can be adjusted to tune thedisplay color without affecting the gamma. For example, if for someapplication, the display needs to have a white point more towards red,the red emission time 122 (or red duty cycle 136) can be increased toprovide more red light.

For illustrative purposes, only one pixel 120 is explicitly shown in theFIG. 1a . It is understood that it is not limited to a particular numberof rows and columns of pixels. For example, a display system can beimplemented with a display screen with a number of rows and columns ofpixels commonly available in displays for mobile devices, monitor-baseddevices, and/or projection-devices. In a multichannel or color display,a number of different types of pixels, each responsible for reproducingcolor of a particular channel or color such as red, green, or blue, willbe present in the display. Pixels of this kind may also be referred toas “subpixels” as a group of them collectively provide a desired colorat a particular row and column of the display, which group of subpixelsmay collectively also be referred to as a “pixel”.

Power Optimization and Dynamic Range Enhancement

Displays configured to display a video feed of moving images typicallyrefresh the display at a regular frequency for each frame of the videofeed being displayed. Displays incorporating an active matrix can allowindividual pixel circuits to be programmed with display informationduring a program phase and then emit light according to the displayinformation during an emission phase. Thus, displays operate with a dutycycle characterized by the relative durations of the program phase andthe emission phase. In addition, the displays operate with a frequencythat is characterized by the refresh rate of the display. The refreshrate of the display can also be influenced by the frame rate of thevideo stream. In such displays, the display can be darkened duringprogram phases while the pixel circuits are receiving programminginformation. Thus, in some displays, the display is repeatedly darkenedand brightened at the refresh rate of the display. A viewer of thedisplay can undesirably perceive that the display is flickeringdepending on the frequency of the refresh rate.

A frame defines the time period that includes a programming cycle orphase during which each and every pixel in the display system isprogrammed with a programming voltage indicative of a brightness and adriving or emission cycle or phase during which each light emittingdevice in each pixel is turned on to emit light at a brightnesscommensurate with the programming voltage stored in a storage element. Aframe is thus one of many still images that compose a complete movingpicture displayed on the display system.

There are at least two schemes for programming and driving the pixels:row-by-row, or frame-by-frame. In row-by-row programming, a row ofpixels is programmed and then driven before the next row of pixels isprogrammed and driven. In frame-by-frame programming, all rows of pixelsin the display system are programmed first, and all of the pixels aredriven at the same time. Either scheme can employ a blanking time at thebeginning or end of each frame during which the pixels are not emittingany light.

For emissive displays, the current of the emissive device is controlledby the pixel circuit to create different grayscales during each framecycle. In one case, the amount of the current is controlled. The mainchallenge with this method is that some emissive devices (e.g.micro-LEDs) have efficiency curves that drops at lower current andhigher current densities. Another method is to control the duration ofthe current applied to the pixel for each grayscale. There are severalissues associated with this approach. However, the main one is thetiming. The high resolution and high frame rate displays cannotaccommodate the timing needed for this approach.

In one embodiment, the frame timing is adjusted so that the emissivedevice is working on optimized current density most of the time. Forexample, if the display is working mainly at a specific brightness, theduty cycles 132, 134, 136 or emission times 122, 124, 126 as shown inFIGS. 1b and 1c can be adjusted so that the emissive device currentdensity is optimized for such brightness. For example, the red emissivedevice optimized current density can be J_(r-opt). If the red pixel ison during the entire frame time at such current density, the display canproduce brightness B_(r-full). If the major red brightness is B_(r-mj),the emissive time 122 can be calculated as T_(f)*B_(r-full)/B_(r-mj)where T_(f) is the frame time. Similarly, one can calculate the dutycycle 132 for red.

In another embodiment, one method to find the major brightness, is touse the peak brightness and the applications. For example, videos aremainly running at 30% of peak brightness.

In yet another embodiment, another method to find the optimize dutycycles 132, 134, 136 and emission times 122, 124, 126 is to evaluate theframe data to find the optimized duty cycle. In one case, the majorbrightness is calculated for the frame to find the proper value for theduty cycles or emission times. In another method, an optimizationalgorithm is run to find a global or a local optimized value for theduty cycles or the emission times. The same method can be used formultiple frames instead of one frame.

In another method, the frame can be divided into several sub frames andthe emission times or the duty cycles that are optimized for each subframes for a power consumption of different ranges of gray scales. Theseoptimizations can be done similar to the one done for a single subframe.

FIG. 2a-2b depicts two examples of power optimized display drivingscheme. A panel driving scheme comprises plurality of sub-frame cyclesin which at least one gray-scale level may be optimized to achieve lowerpower consumption.

In the driving scheme of FIG. 2a , a panel driving scheme 200 acomprises a frame having a plurality of sub-frame cycles such as lowgrayscale emission time 222 l and no emission 208 l for low grayscalesubframe 206 l and high grayscale emission time 222 h and no emission208 h for high grayscale subframe 206 h during a frame time 220. Asillustrated in FIG. 2a , the emission time 222 l, 222 h optimization forboth low and high grayscale ranges is used. Every row of the displayarray is accessed only twice during each frame time 220 to refresh thepixel contents within that row according to the optimized video data.The row access interval may be separated by one or more row times.Accordingly, in this driving scheme, the memory buffer depth requirementmay be limited to the number of rows between two consecutive accessintervals.

In the driving scheme 200 b of FIG. 2b , the duty cycle optimization isused. Here, the duty cycle 232 l and 232 h is optimized for two range ofgrayscales (e.g. low and high) to achieve the lowest power consumption.

According to some examples, a display device may be provided. Thedisplay device may comprising an array of pixels, wherein each pixelcomprising a plurality of subpixels arranged in a matrix and a drivingcircuitry configured to provide an individual emission control signal toeach sub-pixel of each pixel in the array of pixels to independentlycontrol a emission time and a duty cycle of each sub-pixel.

According to another embodiments, the display may further include afirst emission control signal may be provided concurrently to eachsub-pixel of a first color in at least one row of pixels, a secondemission control signal may be provided concurrently to each sub-pixelof a second color in at least the one row of pixels, and a thirdemission control signal may be provided concurrently to each sub-pixelof a third color in at least the row of pixels. The first color may bered, the second color may be green, and the third color may be blue.

Another to some embodiments, the display may further comprising a fourthemission control signal may be provided to each sub-pixel of a fourthcolor in the array of pixels, wherein the fourth color is one of cyan,white, and yellow.

According to further embodiments, the emission control signal may be apulse-width-modulation (PWM) signal and each pixel and sub-pixel may bea micro-light emitting device (LED).

According to yet further embodiments, the first, second and thirdemission control signals may be enabled at a same time or a differenttime during a frame time. The first, second and third emission controlsignals may turned on and off multiple times at different duty cycleduring the frame time.

According to further examples, the emission time or the duty cycle foreach sub-pixel may dynamically adjusted to tune the display device colorand optimize power consumption.

According to some embodiments, a frame data may be evaluated to find theoptimized duty cycle and the emission time. An optimization algorithmmay be employed to calculate a global or a local optimized value for theduty cycle or the emission time for each sub-pixel. The duty cycle maybe optimized for two range of grayscales to achieve the lowest powerconsumption.

According to other embodiments, a method for controlling a pixel circuitof an array of pixel circuits of a display device, the pixel circuitcomprising a plurality of subpixels may include providing an individualemission control signal to each sub-pixel of each pixel in the array ofpixel circuits independently to control an emission time and a dutycycle of the sub-pixels.

According to some embodiments, the emission time or the duty cycle foreach sub-pixel may dynamically adjusted to tune the display device colorand optimize power consumption.

According to another embodiments, a frame data may evaluated to find theoptimized duty cycle and the emission time. an optimization algorithmmay be employed to calculate a global or a local optimized value for theduty cycle or the emission time for each sub-pixel. The duty cycle mayoptimized for two range of grayscales to achieve the lowest powerconsumption.

According to yet other embodiments, the emission control signal may be apulse-width-modulation (PWM) signal. Each pixel and sub-pixel is amicro-light emitting device (LED).

According to some other embodiments, the method may further comprisingproviding a first emission control signal concurrently to each sub-pixelof a first color in at least one row of pixels, providing a secondemission control signal concurrently to each sub-pixel of a second colorin at least the one row of pixels; and providing a third emissioncontrol signal concurrently to each sub-pixel of a third color in atleast the row of pixels.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationscan be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

1. A method to adjust a frame timing in a micro-LED display device, themethod comprising: identifying a specific brightness at which themicro-LED display device operates most of the time; and adjusting dutycycle or emission times to optimize a current density of the micro-LEDdisplay device for the specific brightness.
 2. The method of claim 1,wherein the optimized current density produces a full brightness when acolored pixel is on for an entire frame time.
 3. The method of claim 2,wherein the colored pixel is red, green, or blue.
 4. The method of claim1, wherein an emissive time is a function of the frame, the fullbrightness of a color and a major brightness of a color.
 5. The methodof claim 4, wherein the major brightness of a color is derived from apercentage of peak brightness for an application.